There's just something about stepping outside after a long day indoors. The way the sun beats down on you, the breeze kisses your skin, and the grass embraces your feet is calming and invigorating all at once. Journalist Florence Williams spent months of her life digging into this sensation, traveling the globe to pinpoint what exactly it is about nature that makes the human body light up.

"We think of nature as a luxury, not a necessity. We don't recognize how much it elevates us, both personally and politically," she writes in her bookThe Nature Fix, a riveting recount of her journey released earlier this year. "Without this knowledge, we may not ever fully honor our deep, cranial connection to natural landscapes."

When Williams moved from Colorado to Washington, D.C., a few years back, she couldn't anticipate how much she'd miss the mountain trails and sunrise hikes she was leaving behind. This nature void is what first inspired her to look into the specific way our outdoor environment affects our physical and mental health.

By tracing mankind's interactions with nature across generations and cultures, back to the age of Cleopatra, through the transcendental exploration of Muir and Emerson, all the way to groundbreaking research being done by scientists, physicians, and policymakers of today, she found that the answer couldn't be relegated to a sentence or two. Every aspect of time outside—the sounds, the sights, the smells—plays a part in making us happier, healthier people.

The neuroscience of nature.

The research Williams found was clear: Being outside in greenery calms us down and cheers us up. It reduces our stress levels, increases our productivity, and gives us more energy.

One study out of Japan found that taking a walk in the woods as opposed to the city delivered a 12 percent decrease in cortisol levels, 7 percent decrease in sympathetic (fight-or-flight) nerve activity, and 6 percent decrease in heart rate, not to mention a better mood overall.

And the good news is you don't need to be a hard-core hiker to reap some of these benefits. Even looking out at greenery through a window has been shown to increase productivity, reduce stress, and lessen aggression. Research is now being done to see if exposing stroke victims to patterns in nature can help restore brain function, and a prison in Oregon is using videos of ocean and desert scenes to help inmates calm down.

Blame it on our smartphones and increasingly tight schedules, but in the United States, we're spending less time outside than ever before.

Williams was most surprised to learn how far-reaching nature's influence is. Time outdoors can change not only the way we feel about ourselves but the way others perceive us. "It can make you more civilized in some ways, in terms of making you a more empathetic, more compassionate person. It can make you a better listener and make you feel more connected to your community and to other people around you," she tells mbg. "A lot of that comes from the science of awe, which is a relatively new emotion to be studied, and 70 percent of the time people experience awe, it's from being outside in nature."

The park Rx.

Countries around the world are using these findings to inform their national policies. Williams writes of everything from a National Forest Plan in Korea, which offers prenatal classes in the woods and kindergartens immersed in the forest, to Health Nature Trails in Finland that cues visitors to express gratitude outside with stone altars and small chapels dotted throughout.

"I think there are other countries that are far ahead of us on these topics, and it may be in part because their health care systems believe in prevention," says Williams.

Blame it on our smartphones and increasingly tight schedules, but in the United States, we're spending less time outside than ever before. Nature deficit disorder has become a legitimate diagnosis as the average American spends 93 percent of their lives indoors. According to one poll, 70 percent of moms in the United States remember playing outside every day as a child, but only 26 percent of them can say the same of their kids.

Williams attributes this sudden, dramatic decrease largely to our fixation on technology: "In our parents' day, there really wasn't that much to do indoors, so kids went outside. And now, our kids are kind of addicted. We can find endless entertainment inside the boxes of our homes. But the data is showing that time inside is not very good for our mental health or our physical health. I think people are starting to realize that people aren't really happy or fulfilled when they're inside all the time." However, she sees glimmers of hope for a wilder future. "I'm really heartened to see that it is starting to take off in the United States. I think some of that has been led by the neuroscientists here who are interested in the ideas of creativity and productivity. Those are of course ideas that Americans can get behind."

"I do think we're at a critical time in this research. If people really believe that exposure to nature is critical for being human, and not just a luxury commodity, then we need to fight for it. We need to advocate for it."

How to make your time outside count.

If you, too, are looking to introduce more of Mama Earth's medicine into your life, Williams' advice is simple and straightforward: "Go outside, often, sometimes in wild places. Bring friends or not. Breathe."

When we can engage all of our senses, it's an amazing shortcut to feeling restored.

And living in a city doesn't mean you can't get outside in a restorative way. "I don't think we have to think of nature as being Yosemite: something really grand and dramatic," Williams cautions. "If we can appreciate that even small doses of nature can have a big effect on our mood for the day, we can start to really change the way we spend our time."

Easy ways to get started include eating lunch outside, even in a downtown area that has some trees, and change the way you walk to work or school, choosing a street that has more greenery. When you are in these more natural environments, make an effort to be mindful. "Listen to bird songs, look at patterns in the leaves and trees, literally smell the flowers and the pine needles. When we can engage all of our senses, it's an amazing shortcut to feeling restored."